Choosing the Right Gold Solder Alloy for Hermetic Package Sealing

Indium Gold Preforms

Written By Bernard Leavitt, Indium Corporation


The demand for hermetic packages that house laser diodes is growing, and companies that traditionally made RF/microwave packages are now expanding their businesses into optical packages.

What makes optical package manufacturing unique is the variety of end uses and operational temperatures. As a result, the assembly materials options have to be broad. Gold solder alloys provide low and high temperature options.

Here is a quick overview of the most commonly used gold alloys for package assembly (all eutectic or near-eutectic):

  • 80Au20Sn (280°C): This alloy wets very well in a forming gas atmosphere and has a eutectic melting temperature of 280°C .
  • 88Au12Ge (356°C): This alloy is slightly prone to voiding, so it’s typically not used in glass-to-metal joints. Some companies use 88Au12Ge window frame preforms in the baseplate-to-frame joint. Locating leaks and doing re-work on baseplate-to-frame joints is fairly easy, depending on the size of package.
  • 80Au20Cu (891°C): This is also a eutectic alloy which makes it ideal for braze joints that are dependent on capillary action to fill them, like glass-to-metal joints.

Some company’s reference 80Au20Sn and 88Au12Ge as low-temperature brazes because they are used for hermetic sealing packages with low operating temperatures. 80Au20Sn is commonly used for Kovar lid attachments.

Summary: Gold solder alloys are very important due to their unique range of reflow temperatures and their resistance to corrosion. This makes them ideal for high-reliability optical and laser hermetic package housing assemblies.

If you have any questions or are looking to get some help on a new project, please email me or give me a call.